Bumpers have long been used on vehicles to absorb the impact from low speed collisions. The bumper absorbs the energy of the collision while the vehicle itself remains undamaged. Thus, after a collision, only the bumper needs to be replaced.
Early bumpers were provided with "collapsible zones" which dissipated the energy of collision by deforming upon impact. These early bumpers were usually metal.
Later, bumpers were designed to be made of less expensive materials and to dissipate the energy of collision without destroying the bumper, at least at relatively weak collision forces. Some bumpers have been designed to return to their original shape after collision and deformation. Bumpers have used a variety of means to dissipate collision energy.
The following patents are examples of relevant prior art as it relates to the present invention. U.S. Pat. No. 3,739,882 discloses a shock absorbing device having outer and inner sections and an intermediate section that operates between the inner and outer sections. The intermediate section contains an elastic material to absorb the collision force. The intermediate section returns to its original shape on a delayed basis.
U.S. Pat. No. 3,779,592 discloses a box beam bumper made of a pair of structural members formed from dissimilar metals. Two different metals are used to lower cost and bumper weight while still allowing for strength and resistance to deformation where needed. The dissimilar metals are joined by adhesive layers and/or non-conductive rivets. The dissimilar metals are not allowed to make galvanic contact with each other.
U.S. Pat. No. 3,884,516 discloses an impact-damping bumper comprising a rigid support member secured to a resilient member having high impact-damping capacity. The rigid and resilient members are secured to each other by screws.
U.S. Pat. No. 4,460,205 discloses yet another type of shock absorbing system. German Patent No. 24 57 676 discloses a bumper using rivets to connect a rigid support to a hollow molded plastic bumper strip. Slight impacts cause the non-riveted areas of the strip to bend over, without lasting damage. Only larger impacts shear the rivets, necessitating replacement.
Japanese Patent No. 62-128732 discloses an FRP (fiberglass reinforced plastic) box beam bumper made of two FRP channels joined together. This bumper beam is lightweight, elastic and inexpensive.
U.S. Pat. No. 4,762,352 discloses a vehicle bumper having a shock-absorbing member made of a foamed synthetic resin attached to a steel or FRP backup box beam.
Years of experience have shown that an ideal bumper beam should be lightweight and inexpensive, in addition to having good impact absorbing characteristics. This has led to the use of materials other than steel, for at least the impact absorbing portion of the bumper, as is disclosed in some of the above patents.
It is also sometimes desirable to have a bumper serve as a structural member of the vehicle. Of course, steel or some other strong substance is required for this. Thus, many modern bumpers have both structural and impact absorbing portions, again, as is disclosed in some of the above patents.
The non-steel portions of a bumper cannot be attached to a vehicle until certain operations are done to the car (i.e. oven bonding paint to the frame). This means that if a bumper is also to be used as a structural member of the car, that part of the bumper must be attached to the car early on in the assembly of the car while the other bumper beam components must be added later on.
The impact absorbing components are usually not steel. This reduces weight and cost and allows for the design and implementation of other specific desirable features and characteristics such as spoilers. The non-steel portions of the bumper have previously been bolted or riveted to the structural part of the bumper, near the end of the assembly process. This is inefficient and is not readily adaptable to robotic construction.
Thus, it has become desirable to develop a more efficient method of making a bumper for a vehicle, with structural and impact absorbing portions, where the structural portion of the bumper is attached to the vehicle early in assembly, while the impact absorbing and other portions of the bumper are attached later. This later attachment should be fast, inexpensive and adaptable to robotic installation. The present invention is directed, in part, to these needs.